Composite powder, use in a shaping process, and mouldings produced from this powder

ABSTRACT

The present invention relates to a composite powder which comprises polymer powder and porous glass beads, and to the use of this composite powder for shaping processes, and also to mouldings produced from this composite powder.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of DE 102007019133.4 filed onApr. 20, 2007, the contents of which are incorporated by reference.

FIELD OF THE INVENTION

The invention relates to molded products and compositions useful fortheir manufacture.

DESCRIPTION OF RELATED ART

Rapid provision of prototypes is a task frequently encountered in recenttimes. Particularly suitable processes are those based on pulverulentmaterials, where the desired structures are produced layer-by-layer viaselective melting and hardening. No support structures are needed herefor overhangs and undercuts, since the powder bed surrounding the moltenregions provides sufficient support. There is also no subsequent workneeded to remove supports. The processes are also suitable for short-runproduction.

A process which has particularly good suitability for the purpose ofrapid prototyping is selective laser sintering. In this process,plastics powders are selectively and briefly irradiated with a laserbeam in a chamber, the result being that the powder particles impactedby the laser beam melt. The molten particles coalesce and rapidlysolidify again to give a solid mass. Repeated irradiation of layersconstantly freshly applied can produce three-dimensional bodies simplyand rapidly by this process.

The laser-sintering (rapid prototyping) process for production ofmouldings from pulverulent polymers is described in detail in the patentspecifications U.S. Pat. No. 6,136,948, WO 96/06881 (both DTMCorporation). A wide variety of polymers and copolymers is claimed forthis application, examples being polyacetate, polypropylene,polyethylene, ionomers and polyamide.

Other processes with good suitability are the SIB process as describedin WO 01/38061 and a process as described in EP 1 015 214. Bothprocesses use full-surface infra-red heating for melting of the powder.The selectivity of melting is achieved in the first process viaapplication of an inhibitor, and in the second process via a mask. Afurther process is described in DE 103 11 438. In this process, theenergy needed for fusion is introduced via a microwave generator, andthe selectivity is achieved via application of a susceptor.

Other suitable processes are those using an absorber, either present inthe powder or applied by ink-jet processes, as described in DE 10 2004012 682.8, DE 10 2004 012 683.6 and DE 10 2004 020 452.7.

Pulverulent substrates can be used for the rapid prototyping or rapidmanufacturing processes (RP or RM processes) mentioned, in particularpolymers, preferably selected from polyester, polyvinyl chloride,polyacetal, polypropylene, polyethylene, polystyrene, polycarbonate,poly(N-methylmethacrylimides) (PMMI), polymethyl methacrylate (PMMA),ionomer, polyamide, or a mixture thereof.

WO 95/11006 describes a polymer powder suitable for laser sintering,which when melting behaviour is determined via differential scanningcalorimetry at a scanning rate of from 10 to 20° C./min exhibits nooverlap of the melting peak and recrystallization peak, and which has adegree of crystallinity of from 10 to 90%, likewise determined via DSC,and a number-average molecular weight Mn of from 30 000 to 500 000, andwhose Mw/Mn quotient is in the range from 1 to 5.

DE 197 47 309 describes the use of a nylon-12 powder with increasedmelting point and increased enthalpy of fusion, obtained viareprecipitation of a polyamide previously prepared via ring-opening andsubsequent polycondensation of laurinlactam. This is a nylon-12.

DE 102004003485 describes the use of particles with at least one cavityin layer-construction processes. All of the particles here comprise atleast one cavity, and the particles comprising the cavity are melted viainput of electromagnetic energy.

Powders described above are sometimes provided with glass beads forreinforcement. Since considerable proportions of reinforcing materialhave to be used here to achieve any effect, the density of the componentincreases markedly, as also does that of the powder mixture.Furthermore, handling of these powder mixtures often leads to demixingphenomena, the result being that the mechanical properties that thereinforcing material is intended to achieve are not always constant. Theregions in which the proportion of glass beads is excessive become verybrittle and thus unusable, and the regions in which too few glass beadsare present are softer than intended. The demixing arises from thedifferent density of the polymer particles and of the glass beads, andtends to become evident to some extent whenever the powder mixture istransported or handled. In particular, if powder handling is automatedin the rapid manufacturing process the result can be difficulty incontrolling deviations of properties in the components produced.

SUMMARY OF THE INVENTION

One embodiment of the invention is composite powder comprising at leastone polymer powder and porous glass beads. The polymer powder can be atleast one of nylon-11 powder and nylon-12 powder.

Also embodied herein is where the average particle diameter of the atleast one polymer powder is from 30 to 120 μm, from 40 to 100 μm, and/orfrom 45 to 70 μm.

Also embodied herein is where the ratio of the average particle diameterof the at least one polymer powder to the porous glass beads is from1.5:1 to 10:1, from 1.7:1 to 5:1 and/or from 2:1 to 3:1.

Also embodied herein is where the ratio by weight of the porous glassbeads to the at least one polymer powder is from 1:10 to 20:10, from2:10 to 15:10, and/or from 5:10 to 12:10.

The invention also provides a process for the production of mouldingswhereby at least one layer of at least one composite powder as describedin the preceding paragraphs and further described herein is provided andthen at least one region of the at least one layer is melted withelectromagnetic energy, and wherein at least one other region is notmelted. The inhibition of melting can be accomplished by providing oneor more of a susceptor of the electromagnetic energy, an inhibitor ofthe electromagnetic energy, an absorber of the electromagnetic energy,and/or a mask for the electromagnetic energy.

Mouldings produced by this process are also embodied herein.

DETAILED DESCRIPTION OF THE INVENTION

It was therefore an object of the present invention to provide acomposite powder which permits production of minimum-weight mouldingswhich at the same time have a relatively high modulus of elasticity, byprocessing methods that have maximum reproducibility. The othermechanical properties obtained are not to be poorer than those of acomparable polymer powder with glass beads according to the prior art.The processing method here is a layer-by-layer process in which regionsof the respective powder layer are selectively melted by means ofelectromagnetic energy and, after cooling, have bonded to give thedesired moulding.

Surprisingly, it has now been found, as described in the claims, thatthe use of porous glass beads as reinforcing material alongside apulverulent polymer can produce composite powders from which mouldingscan be produced via a layer-by-layer process in which regions of therespective powder layer are selectively melted, where these haveadvantages in respect of density and tendency towards warpage, togetherwith better properties in respect of consistent processing then using areinforced polymer powder of the prior art, for example the commerciallyavailable materials Duraform GF or EOSINT 3200 GF.

The invention relates to a composite powder based on a pulverulentpolymer with glass beads, the powder having advantages with respect tostability of the production process and with respect to density, and tothe use of this composite powder in shaping processes, and also tomouldings produced via a layer-by-layer process which selectively meltsregions of a powder layer, using this powder. After cooling andhardening of the regions previously melted layer-by-layer, the mouldingcan be removed from the powder bed. The inventive mouldings moreoverhave less tendency towards warpage than conventional mouldings.

The selectivity of the layer-by-layer processes here can by way ofexample be achieved by way of application of susceptors, of absorbers,or of inhibitors, or via masks, or by way of focused energyintroduction, for example a laser beam, or by way of glass fibres. Theenergy input is achieved by way of electromagnetic radiation.

The composite powder is only partially melted in the inventive process.The inventive reinforcing material is encapsulated by the polymer powderwhich is melted via electromagnetic energy input, and after cooling ofthe polymer component a moulding is formed which comprises polymer and,embedded therein, reinforcing material.

It is preferable here that the particles of the reinforcing materialare, like the particles of the polymer component, approximately round.

The average particle diameter of the polymer component is from 30 to 120μm, preferably from 40 to 100 μm and particularly preferably from 45 to70 μm. In a particularly preferred embodiment of the composite powder,it has been found that the particle diameter of the reinforcing materialshould be smaller than that of the polymer component. Preference isgiven to a ratio of average diameter of the polymer particles to theaverage particle diameter of the reinforcing-material particles of from1.5:1 to 10:1, particularly from 1.7:1 to 5:1, and in particular from2:1 to 3:1.

The proportion here by weight of reinforcing material, based on polymercontent, is from 1:10 to 20:10, preferably from 2:10 to 15:10, andparticularly preferably from 5:10 to 12:10.

The density of the composite component here according to the inventionis lower than for a component produced from composite powder accordingto the prior art. An advantage of this is that parts can be producedwith lightweight construction, where the reinforcing action does notsimultaneously generate disadvantages in relation to increased weight.

Another subject matter of the present invention is mouldings producedvia a layer-by-layer process which selectively melts regions of therespective layer, characterized in that they comprise at least onepolymer and also one reinforcing material, and in that the density ofthe inventive composite component here has been lowered with respect toa component produced from composite powder of the prior art. Thetendency towards warpage of the inventive composite components haslikewise been reduced.

An advantage of the inventive composite powder is when it is used in alayer-by-layer process in which regions of the respective layer areselectively melted the mouldings produced have lower density and lesstendency towards warpage than mouldings made from conventional compositepowders. When compared with conventional composite powders, theinventive powder here reduces process risk; there is markedly lessdanger of demixing.

The mechanical properties of the mouldings produced from the inventivecomposite powder here are good and similar to those of the mouldingsproduced from conventional composite powder.

The inventive composite powder is described below, with no intention torestrict the invention thereto.

A feature of the inventive composite powder for processing in alayer-by-layer process in which regions of the respective layer areselectively melted is that the powder comprises at least porous glassbeads and a pulverulent polymer, preferably a polyamide, particularlypreferably a nylon-11 or -12.

The polymer component can comprise amorphous or semicrystalline polymersor a mixture thereof. Examples that may be mentioned without restrictingthe invention thereto are polyester, polyvinyl chloride, polyacetal,polypropylene, polyethylene, polystyrene, polycarbonate,poly(N-methylmethacrylimides) (PMMI), polymethyl methacrylate (PMMA),ionomer, polyamide or a mixture thereof. The polymer component isconverted to the powder form via processes of the prior art, for examplevia milling, spray drying, precipitation or other suitable processes.Sieving or classification can then be advantageous. Post-treatment in amixer with high shear, preferably at temperatures above the glasstransition point of the respective polymer, can also follow, in order toround-off the particles and thus improve powder-flow capability.

One preferred embodiment uses PA11 or PA12 or a mixture thereof aspolymer component of the inventive composite powder.

It is particularly preferable that the polymer component comprisesparticles obtained by way of example via a process according to DE 29 06647 B1 or via DE 197 08 146. The polyamide is dissolved in ethanol andcrystallized out under particular conditions. If appropriate, thematerial is subjected to precautionary sieving and furtherclassification or low-temperature milling.

The bulk density of the polymer powder alone is typically from 220 to600 g/l.

Surprisingly, it has been found that the disadvantages, in particularthe demixing of the components, of a composite powder of the prior artduring the construction process, and also during the up- and downstreampowder-transport processes, can be eliminated if the reinforcingcomponent has porous glass beads. The construction process can thereforeproceed with markedly less risk and more reproducibility, and it ispossible to produce mouldings with constant quality and lower densityand less tendency towards warpage.

It is preferable here that the particles of the reinforcing materialare, like the particles of the polymer component, approximately round.

The average particle diameter of the polymer component is from 30 to 120μm, preferably from 40 to 100 μm and particularly preferably from 45 to70 μm. In a particularly preferred embodiment of the composite powder,it has been found that the particle diameter of the reinforcing materialshould be smaller than that of the polymer component. Preference isgiven to a ratio of average diameter of the polymer particles to theaverage particle diameter of the reinforcing-material particles of from1.5:1 to 10:1, particularly from 1.7:1 to 5:1, and in particular from2:1 to 3:1.

The proportion here by weight of reinforcing material, based on polymercontent, is from 1:10 to 20:10, preferably from 2:10 to 15:10, andparticularly preferably from 5:10 to 12:10.

The reinforcing material comprises porous glass beads. They are alsoknown as expanded glass. The production process adds a blowing agent toproduce granules or particles at high temperature. This process producesmainly round particles with irregular surface, with very fine porestructures in the interior. The result is, based on density, improvedmechanical properties in comparison with solid glass beads or hollowglass beads. For the inventive use it can be advantageous to fractionatethe expanded glass beads. The bulk density of this component alone isusually from 250 to 600 g/l. Surprisingly, it has now been found thatthese advantages of the expanded glass can also be retained in aninventive composite powder and in an inventive process, and also inmouldings. Furthermore, the good thermal insulation of the reinforcingmaterial leads to a reduced tendency towards curl in the constructionprocess.

The low density of the glass beads has an advantageous effect. Mouldingsfor lightweight construction can now be produced as described above withmouldless processes. This opens up new application sectors. Anotheradvantage of the porous glass beads is the irregular surface. This cangive mechanical interlocking between the surface and the polymercomponent, which is advantageous for mechanical properties. Glass beadsused in composite powders of the prior art usually have a relativelysmooth surface and no fine pores, and also have markedly higher bulkdensity.

In one embodiment, the reinforcing component of the composite powdercomprises an expanded glass provided with a size.

The porous glass beads are obtainable, for example, from Dennert PoraverGmbH in Schlüsselfeld, Germany.

The polymer component and the reinforcing component and any furtherauxiliaries are preferably mixed in a dry-blend mixture of the priorart.

Inventive composite powder can moreover comprise auxiliaries and/orfurther organic or inorganic pigments. Examples of these auxiliaries canbe powder-flow aids, e.g. precipitated and/or fumed silicas.Precipitated silicas are marketed, for example, as Aerosil with variousspecifications by Degussa AG. It is preferable that inventive compositepowder comprises less than 3% by weight, preferably from 0.001 to 2% byweight, and very particularly from 0.05 to 1% by weight, of theseauxiliaries, based on the entirety of the polymers present. The pigmentscan, for example, be titanium dioxide particles based on rutile(preferably) or anatase, or can be carbon black particles.

It is also possible to mix conventional polymer powders with inventivecomposite powders. The process for preparation of these mixtures can befound, for example, in DE 34 41 708.

To improve processability, or for further modification of the compositepowder, these can receive additions of inorganic foreign pigments, e.g.transition metal oxides, stabilizers, e.g. phenols, in particularsterically hindered phenols, flow agents and powder-flow aids, e.g.fumed silicas. It is preferable that the amount of these substancesadded to the polymers, based on the total weight of polymers in thepolymer powder, is such as to give compliance with the statedconcentrations for auxiliaries for the inventive polymer powder.

The present invention also provides processes for the production ofmouldings via layer-by-layer processes in which regions of therespective layer are selectively melted, in which inventive compositepowders are used, which are characterized in that these comprise atleast one polymer powder and porous glass beads.

The energy is introduced via electromagnetic radiation, and theselectivity is introduced, for example, via masks, application ofinhibitors, of absorbers, or of susceptors, or else focusing of theradiation, for example via lasers. The electromagnetic radiationencompasses the range from 100 nm to 10 cm, preferably from 400 nm to 10600 nm, or from 800 to 1060 nm. The source of the radiation can, forexample, be a microwave generator, a suitable laser, a radiant heatsource, or a lamp, or else a combination thereof. After the cooling ofall of the layers, the inventive moulding can be removed.

The examples below of these processes serve for illustration, with nointention that the invention be restricted thereto.

Laser sintering processes are well known and are based on the selectivesintering of polymer particles, where layers of polymer particles arebriefly exposed to laser light, and the polymer particles exposed to thelaser light are thus bonded to one another. Three-dimensional objectsare produced via successive sintering of layers of polymer particles.Details of the selective laser sintering process are found, for example,in the specifications U.S. Pat. No. 6,136,948 and WO 96/06881.

Other processes with good suitability are the SIB process as describedin WO 01/38061 and a process as described in EP 1 015 214. Bothprocesses use full-surface infra-red heating for melting of the powder.The selectivity of melting is achieved in the first process viaapplication of an inhibitor, and in the second process via a mask. Afurther process is described in DE 103 11 438. In this process, theenergy needed for fusion is introduced via a microwave generator, andthe selectivity is achieved via application of a susceptor.

Other suitable processes are those using an absorber, either present inthe powder or applied by ink-jet processes, as described in DE 10 2004012 682.8, DE 10 2004 012 683.6 and DE 10 2004 020 452.7.

A feature of the inventive mouldings, which are produced via alayer-by-layer process in which regions are selectively melted is thatthey comprise at least one polymer, and also a reinforcing material, andthat the density of the inventive composite components here is reducedin comparison with that of a component produced from composite powder ofthe prior art, and tendency towards warpage is reduced.

The mouldings can moreover comprise auxiliaries (and the statements madefor the polymer powders apply here), examples being heat stabilizers,e.g. sterically hindered phenol derivatives. Inventive mouldingspreferably comprise less than 3% by weight, particularly preferably from0.001 to 2% by weight, and very particularly preferably from 0.05 to 1%by weight, of these auxiliaries, based on the entirety of the polymerspresent.

Application sectors for these mouldings can be found not only in rapidprototyping but also in rapid manufacturing. The latter certainly meanssmall production runs, i.e. production of more than one identical part,but where production by means of an injection mould is notcost-effective. Examples here are parts for high-specification carswhere the number of units produced is only small, or replacement partsfor motor sports, where the important factors are not only the smallnumber of units but also the lead time.

Industries using the inventive parts can be the aerospace industry,medical technology, mechanical engineering, automobile construction, thesports industry, the household goods industry, the electrical industryand the lifestyle sector.

The examples below are intended to describe the inventive compositepowder and its use, without restricting the invention to the examples.

The laser scattering values measured were obtained with a MalvernMastersizer S, Version 2.18. Bulk density was determined by an apparatusto DIN 53466.

The examples below are intended to illustrate the invention but not torestrict it.

Comparative Example Non-Inventive Composite Powder

100 parts of EOSINT PA2200 from EOS GmbH are mixed in an MTI mixer (500rpm, 5 minutes) with 40 parts of Spheriglass E-2000 glass beads fromPotters Ballotini. These are compact glass beads whose BET surface areais below 1 m²/g and whose particle size is smaller than 100 μm, density2.5 g/cm³.

Inventive Example 1 Composite Powder with Expanded Glass Beads from 40to 125 μm

100 parts of EOSINT PA2200 from EOS GmbH are mixed in an MTI mixer (500rpm, 5 minutes) with 30 parts of Poraver expanded glass beads fromDenner Poraver GmbH. These are porous glass beads whose bulk density is530 kg/m³ and whose particle size is smaller than from 40 to 125 densityabout 1.0 g/cm³.

Processing of Composite Powders:

All of the powders were used for a construction process in an EOSINTP360 from EOS GmbH, Krailling, Germany. This is a laser-sinteringmachine. The construction chamber was preheated up to almost the meltingpoint of the respective specimen. The parameters for the laser, such asvelocity and power, were adapted to each material via trials.

As can be seen from Table 1 below, the inventive test specimens exhibitmarked advantages in particular in relation to density while othermechanical properties are in essence unaltered. The different degrees ofreinforcement here have to be considered. Based on component density,mechanical properties have been improved.

The inventive components moreover exhibit markedly less warpage. Nor didany demixing effects occur during the construction process.

TABLE 1 Comparative Inventive example Example 1 Modulus of 2959 2545elasticity Density [g/l] 1.26 1.01 E-modulus, 2348 2519 based on densityStandard (13 specimens) (5 specimens) deviation in % 7.5% 2.7% E-modulus

1. A composite powder comprising at least one polymer powder and porousglass beads.
 2. The composite powder of claim 1, wherein the at leastone polymer powder is at least one of nylon-11 powder and nylon-12powder.
 3. The composite powder of claim 1, wherein the average particlediameter of the at least one polymer powder is from 30 to 120 μm.
 4. Thecomposite powder of claim 1, wherein the average particle diameter ofthe at least one polymer powder is from 40 to 100 μm.
 5. The compositepowder of claim 1, wherein the average particle diameter of the at leastone polymer powder is from 45 to 70 μm.
 6. The composite powder of claim1, wherein the ratio of the average particle diameter of the at leastone polymer powder to the porous glass beads is from 1.5:1 to 10:1. 7.The composite powder of claim 1, wherein the ratio of the averageparticle diameter of the at least one polymer powder to the porous glassbeads is from 1.7:1 to 5:1.
 8. The composite powder of claim 1, whereinthe ratio of the average particle diameter of the at least one polymerpowder to the porous glass beads is from 2:1 to 3:1.
 9. The compositepowder according to of claim 1, wherein the ratio by weight of theporous glass beads to the at least one polymer powder is from 1:10 to20:10.
 10. The composite powder of claim 1, wherein the ratio by weightof the porous glass beads to the at least one polymer powder is from2:10 to 15:10.
 11. The composite powder of claim 1, wherein the ratio byweight of the porous glass beads to the at least one polymer powder isfrom 5:10 to 12:10.